FIG. 1 depicts a conventional projector 100, for projecting an image generated by, for example, a computer or television signal. Projector 100 includes an illumination path 110, a transmissive spatial light modulator (SLM) 120, and a projection path 130. These elements combine to project an image onto a surface 140. In operation, light source 112 shines an illuminating beam 114 (depicted as dashed lines) through collimating optics 116 and a polarizer 118 in illumination path 110 to impinge upon SLM 120.
SLM 120 is controlled by an image signal, and modulates the polarity of light corresponding to individual image pixels in the polarized beam. The modulated beam then passes to an analyzer 132, a polarizing filter oriented to pass only light of a selected polarity.
SLM 120 establishes the intensity of individual pixels by modulating the polarity of light corresponding to each pixel. SLM 120 represents a bright pixel by modulating the polarity of light representing that pixel to allow analyzer 132 to pass that light: SLM 120 represents a dark pixel by modulating the polarity of light representing that pixel to allow analyzer 132 to block that light. Intermediate degrees of polarity modulation offer intermediate levels of brightness. The analyzed beam then passes through projection optics 134 to a surface 140. Projector 100 thus projects an image specified using SLM 120 onto surface 140 (e.g., a wall).
Projector 100 suffers from considerable loss of light due to the presence of drive electronics (not shown) necessarily located at each pixel element of SLM 120. This deficiency has been addressed using reflective SLMs in which the drive electronics are grouped on one side of the light valve. A conventional reflective-SLM projector 200 is depicted in FIG. 2.
Projector 200 of FIG. 2 includes an illumination path 210, a reflective SLM 220, and a projection path 230. A light source 212 shines an illuminating beam 214 (depicted as dashed lines) through collimating optics 216 into a polarizing beam splitter 218. Beam splitter 210 polarizes illuminating beam 214 and reflects the polarized beam onto SLM 220. SLM 220 then modulates and reflects the polarized beam back through beam splitter 218, which analyzes the reflected beam using the same interface that initially polarized illuminating beam 214. The analyzed beam then passes through projection optics 234 to a surface 240. Projector 200 thus projects an image specified using SLM 220 onto surface 240 (e.g., a wall).
Using beam splitter 218 as both a polarizer and an analyzer does not allow optimum placement of the polarizer and analyzer, but instead requires a compromise. In addition, beam splitter 218, being relatively thick, and being required to act both as a polarizer and a beamsplitter results in a relatively expensive component.
In light of the foregoing deficiencies in the prior art, there is a need for a color separation and recombination system that reduces light loss, image distortion and enables the use of inexpensive thin film polarizers as the polarizing elements.